Gateway GPRS support node (GGSN):

The GGSN is also a functional entity that provides packet data services. It routes
and encapsulates packet data between the GPRS/UMTS network and an external PDN.

The
GGSN provides the following functions:

• Interface to an
       external PDN


• GPRS session
       management


• FA functions


• Charging for
       postpaid services


• Call control and
       service switching functions for prepaid services